Physical Model for Thermal Stress‐Induced Phase Transition of Octogen in Polymer‐bonded Explosives

ABSTRACT The β→δ phase transition of cyclotetramethylene tetranitramine (octogen, HMX) significantly impacts the thermal and impact safety of HMX‐based polymer‐bonded explosives (PBXs). HMX demonstrates varying phase transition temperatures when combined with different additives. To date, there has been a lack of systematic research regarding the mechanisms by which additives influence these transition temperatures. This study investigates the phase transition temperature of HMX within PBXs using X‐ray diffraction (XRD) techniques. A mathematical model has been developed to describe the interactions between the binder and HMX, effectively elucidating the underlying influence mechanisms. The predicted phase transition temperatures align closely with the results obtained from XRD analysis. It was observed that HMX crystals and additives undergo expansion upon heating, leading to alterations in the phase transition temperatures of HMX induced by thermal stress. Additionally, a physical model has been constructed to account for the phase transitions induced by thermal stress.